Have you checked the fuel filter?? check intake gaskets for leaks. Meybe need to clean carb. Most of the late model carbs dont have much of a adjustment. Having to run with the choke on points to a fuel problem somewhere.
The engine needing choke to run means it is not getting enough fuel. This can be caused by an air leak (too much airl) or could be a blockage in the carb (not enough fuel). Most carbs nowdays dont have adjustments to richen them up. Most likely the small jet or low speed circuit is clogged. The smallest passageway in the carb usually gets clogged first so I would look there.